1. Field of the Invention
The present invention relates to a method for producing a magnetic tape. More specifically, the present invention relates to improvement of disorder of a wound form of a magnetic tape wound around a tape reel. The present invention further relates to a magnetic tape whose wound form is improved, and to a method for improving a wound form of a magnetic tape. The present invention is based on Japanese Patent Application No 2004-38337, filed on Feb. 16, 2004 the disclosure of which is incorporated herein by reference.
2. Description of the Related Art
In conventional, audio tapes, video cassette tapes, memory tapes, video tapes for broadcasting and other tapes are utilized as recording media in various fields. Also, as shown in FIG. 14, a magnetic tape cartridge has been well-known as recording media having a large capacity, in which a magnetic tape MT wound around a single tape reel 10A is stored (see, for example, Japanese Patent Laid-Open Publication No.11-265560).
All of the magnetic tapes used in these recording media are typically utilized in the state that they are wound around a tape reel 10 (or 10A) as shown in FIG. 1, FIG. 7, FIG. 8, and FIG. 14. FIG. 1 is an exploded perspective view showing one example of a recording medium utilizing a tape reel 10, FIG. 7 is a perspective view showing one example of a tape reel 10, FIG. 8 is a cross-sectional view of FIG. 7 taken along a line A-A, and FIG. 14 is a perspective view of a magnetic tape cartridge in which one tape reel is stored.
For example, as shown in FIG. 7 and FIG. 8, a tape reel 10 is composed of a cylindrical hub 11, a pair of disk-shaped flanges 12 and 13 (upper flange 12 and lower flange 13) fixed onto the hub 11 in a facing manner parallel to a lower end 11a and an upper end 11b of the hub 11, and the tape reel 10 winds the magnetic tape MT around an outer circumference 11c of the hub 11. At a time of winding or feeding the magnetic tape MT, the upper flange 12 and the lower flange 13 regulate positional variation of the magnetic tape MT in its width direction through an inner surface 12a of the upper flange 12 and an inner surface 13a of the lower flange 13 to serve the function of stabilizing the driving of the magnetic tape MT.
A distance between the upper flange 12 and the lower flange 13 is set to be slightly wider than the width of the magnetic tape MT in order to prevent either of tape edges E1 and E2 from being damaged due to collision with either of the inner surface 12a of the upper flange 12 and the inner surface 13a of the lower flange 13 at a time of winding or feeding the magnetic tape MT. For example, in FIG. 8, the magnetic tape MT is wound around the hub 11 in the state that the tape edge E1 is in contact with the inner surface 12a of the upper flange 12 and, thus, clearance is provided between the tape edge E2 of the magnetic tape MT and the inner surface 13a of the lower flange 13.
In the case where the clearance is provided between the tape edge E2 of the magnetic tape MT and the inner surface 13a of the lower flange 13 as shown in FIG. 8, in some cases, parts of the magnetic tape MT would be projecting from the tape edge E2 into the clearance, whereby so-called “disordered winding” would occur in which the tape edge E2 becomes uneven as shown in FIG. 9.
If disordered winding occurs, the position of the magnetic tape MT in the width direction of the magnetic tape is varied, driving the magnetic tape MT in an unstable manner. This would bring about servo tracking abnormality or such, making it difficult to maintain good recording/reproducing characteristics of the magnetic tape.
If disordered winding occurs, the tape edges E1 and E2 are easily damaged during the course of transfer, posing a problem in terms of quality control. In particular, in the case of video tape, which records sound data in the vicinity of the tape edge E1 or E2, a problem would occur in that sound cannot be surely outputted at the time of reproduction.
Particularly, in the magnetic tape cartridge 1A (see FIG. 14 for the magnetic tape cartridge) composed of magnetic tape MT wound around the tape reel 10 (see FIG. 8) as disclosed in Japanese Patent Laid-Open Publication No. 11-265560, according to increasing of the capacity and density, the thickness of the magnetic tape becomes much thinner, and the surface of the magnetic tape becomes much more flattened.
This leads to the situation where disordered winding occurs much more frequently at the time of driving the magnetic tape by means of a drive. Also, at the time of the production, disorder of the magnetic tape when the tape is wound around a winder (not shown) tends to occur more often.
Various causes can be considered for disorder of wound tape, one of which is the fact that when the magnetic tape MT is wound around the hub, the magnetic tape MT is slid in the width direction due to the air entering between the magnetic tape.
Particularly, it has been experimentally known that in a production stage for producing the magnetic tape cartridge 10 shown in FIG. 10, which comprises the tape reel 10A as a constituting part, if the speed for winding the magnetic tape 10A is set at a high level (for example, 10 to 20 m/s) in order to enhance the productivity, the occurrence of disordered winding significantly increases.
Other factors for causing disordered winding, which can be considered, are (1) the magnetic tape MT is irregularly curved in the width direction; (2) tension distribution loaded to the magnetic tape MT is biased, (3) due to the magnetic tape being stored in a state of disordered winding, the winding form of the magnetic tape is deformed or such.
As shown in FIG. 15A, it has hitherto been known that when the magnetic tape MT is wound around a hub 110 of a tape reel 100, a rotating endless belt 200, which is made of an elastic material such as rubber supported by rotating rollers 210, 220, and 230, is pushed onto the surface of the magnetic tape MT to allow the air entering in spaces of the magnetic tape MT for escaping therefrom whereby the disordered winding of the magnetic tape is decreased. Also, as shown in FIG. 15B, it has also been known that a touch roll 300 made of an elastic material such as rubber is used instead of the endless belt 200.
In addition, Japanese Patent Laid-Open No. 1-313283 discloses that as shown in FIG. 16A, a magnet 190 comprising concentrically divided inner region 191 and outer region 192 where in both regions 191 and 192, end surfaces facing to the end line of the tape are hetero poles, and the magnetic tape MT is wound while attracting it to a flange of a tape reel 130 by a magnetic force “i” possessed by the magnet 190, to thereby change the winding form for the better. The invention disclosed therein exhibits excellent effects in terms of changing the winding form of the magnetic tape at the time of the production for the better.
However, while the technique disclosed in Japanese Patent Laid-Open No. 1-313283 can change the winding form of the magnetic tape at the time of the production for the better, i.e., can prevent the disordered winding at the time of the production, disordered winding still occurs after the magnetic tape has been purchased and used by a user.
On the other hand, according to the invention disclosed in Japanese Patent Laid Open No. 9-138945, a tapered winding surface 91 is formed on a winding shaft 90 where the shaft diameter of one end (long winding shaft 90a) is different from that of the other end (short winding shaft 90b) (See FIG. 16B), the magnetic tape MT is wound around the winding shaft 90, the magnetic tape MT, which is in the wound state, is left standing over a prescribed period of time whereby the magnetic tape falls into the habit of winding. According to the invention disclosed therein, the product excels in terms of capability of preventing the magnetic tape from disordered winding even after the product has been distributed to a user.
However, in the conventional methods shown in FIG. 15A and FIG. 15B, since abrasion powder occurs due to direct contact of the endless belt 200 or the touch roll 300 with the magnetic tape MT, the contact with the magnetic tape MT is preferably reduced as little as possible.
In the invention disclosed in Japanese Patent Laid Open No. 1-313283-138945 shown in FIG. 16A, the problem remains that the technique is not applicable, if the thickness of the magnetic tape MT becomes thinner.
In the invention disclosed in Japanese Patent Laid Open No. 9-138945 shown in FIG. 16B, a long period is required for the magnetic tape MT to assume a winding habit, which is not preferred in terms of productivity.
The present invention has been made in light of the situation mentioned above, and an object of the present invention is, therefore, to provide techniques in which a prescribed winding habit is imparted to the magnetic tape at the time of production, whereby the disordered winding is prevented during the course of the production and shipping the product, and which makes it difficult to generate disordered winding after the product is used by a user (such as a method for producing a magnetic tape, a magnetic tape itself, and a method for improving the winding form of the magnetic tape)